Carrier tapes are of ever increasing importance in assembly operations in numerous industries including, in particular, the electronics and pharmaceutical industries. The tapes are used, for example, to transport miniature and subminiature electronic components from a component manufacturer to a customer's assembly station where automatic equipment functions to remove the component from the carrier tape and mount the component to a circuit board or the like. The carrier tape (or transfer tape, as it is sometimes referred to) may also function to bring different components to an assembly station in proper order for sequential assembly.
Such carrier tapes are often in the form of a base strip of plastic, paper, or foil which is usually covered by a cover strip sometimes called top tape. The base strip is formed with a plurality of cavities or pockets for the components and the cover strip is secured to the base strip to thereby prevent the components from prematurely falling out of the cavities. In the past the base strip and cover strip were most commonly held in place by an adhesive, heat bond or spaced snap-type fasteners. Typical examples of prior art carrier tapes are disclosed in U.S. Pat. Nos. 3,465,874; 3,650,430; 3,700,019; 3,894,896; 3,910,410; and 4,298,120. The previously mentioned application Ser. Nos. 008,293 and 913,131 disclose carrier tapes which utilize a continuous mechanical interlock between the base strip and cover strip which obviates many of the problems associated with the use of the various prior art methods of securing the base strip and cover strip.
To function properly, a carrier tape must securely convey its cargo as required and then, at the proper location, be capable of being quickly and positively opened so that the component may be easily removed for assembly purposes. The tape should afford a degree of protection for the sensitive components to be conveyed therein with respect to contamination, electro-static discharge, temperature change and mechanical shock. In addition, the seal or bond between the tape components must be releasable to a known and consistent value at the unloading point to insure that only the required length of base tape will be exposed.
Prior art tapes utilizing heat activated adhesives or heat bonding techniques present a risk of adhesive residue contamination of the component. In addition, such tapes cannot be readily opened and reclosed for quality testing or the like and present difficulties in aligning the cover and base strips. Further, heat bonding requires the use of relatively high temperatures which may be harmful to the components to be carried. In addition, the use of static-dissipative or conductive additives to prevent or dissipate the build-up of electrostatic charges tend to interfere with the bonding characteristics of the adhesives used.
In view of the above, it is the principal object of the present invention to provide an improved carrier tape construction which avoids the use of adhesive and chemical bonding and in which the cover strip and base strip are uniformly and consistently secured to one another yet which can readily and positively be separated from one another.
A further object is to provide a tape construction wherein the cover and base strips automatically align with each other during assembly and which, if necessary, may be opened and reclosed.
Another object is to provide such a tape which may readily be used on existing equipment with little or only minor modification.
A still further object is to provide a simple and reliable mechanism for properly securing the base and cover strips of such a carrier tape to each other.
Still another object is to provide a simple and reliable mechanism for properly separating the base and cover strips of such a carrier tape from one another.